1. Technical Field
The present invention is related to rabies vaccines More particularly, the present invention is related to a rabies vaccine provided by the establishment of a host organism as a substrate for inserting and expressing genetic information of other organisms.
2. State of the Art
Raccoon pox virus (RCN) was first isolated from upper respiratory tissues of two apparently healthy raccoons captured in 1961-62. The raccoons were captured during a survey of local wildlife at Aberdeen Proving Grounds, Maryland. This was reported by Herman, Y.F Bacteriol. Proc., 64th Ann. Meet. Amer. Soc. Microbiol. 1964 page 117, and Alexander. A.D. et al., J. Wildlife Dis. 1972:8:119-126. No gross lesions were seen during necropsy of the two raccoons. The sera of 22 of 92 raccoons from the same area showed raccoon poxvirus hemagglutinating-inhibiting (III) antibodies. This indicated the presence of the virus in nature at that time. The current distribution of RCN virus in nature is unknown. The biological characteristics of one isolate, including its DNA restriction map and its pathological innocuity when inoculated into raccoons, has been described by Thomas E.K. et al., Arch. Virol. 1975:49:217-227; Esposito J.J. & Knight J.C. Virology 1985:143:230-251; and Parsons B.L. & Pickup D.J. Virology 1987:161:45-53. In an earlier study by Esposito, J J. & Knight, J.C. Virology 1985:143:230-251 it was observed that thyymidine kinase (TK) nucleotide sequences within the DNA fragment Hind3-J of vaccinia virus cross hybridized with raccoon poxvirus DNA fragment Hind3-E. Chimeric plasmids like those designed for inserting rabies virus surface spike glycopiotein (G protein) coding sequences into the vaccinia virus TK region were reported by Esposito et al., Virus Genes 1987:1:7-22 and Esposito, J.J. Brechling, K. Moss, B. Patent Application No. 07/010,424, filed on Mar. 25, 1987.
In the United States, the wildlife species most involved in rabies transmission are skunks, raccoons, foxes, and insectivorous bats. Raccoons currently rank second to skunks as the major reservoir. Rabid foxes are a major source of the disease in Canada and many European countries. With the discontinued use of poisoning and trapping in the 1960s, attempts have been made to protect foxes from rabies via bait-delivered oral vaccination. The immunization of foxes by the feeding of live-attenuated rabies virus vaccine in sausages is disclosed by Baer, G.M. et al, Am. J Epidemiol. 1971:93:487-490 and the corresponding U.S Pat. No. 4,014,991. This form of immunization led to efficacy and safety studies of live-attenuated rabies vaccine in chicken head baits as described in the World Health Organization Expert Committee on Rabies 7th Report, 1984 Technical Report Series 709, WHO, Geneva. The virtual elimination of rabies in Switzerland and field trials in West Germany and other countries have indicated that oral-bait rabies vaccines can significantly curtail the spread of rabies. Although live-attenuated rabies virus vaccines are effective in immunizing foxes against rabies, they are not effective for immunizing skunks and raccoons.
A live recombinant vaccinia virus has been developed that expressed the G protein of rabies virus strain ERA and that induced rabies virus-neutralizing antibodies and protection against a rabies challenge. This is disclosed in the articles Wiktor, T.J. et al., PNAS 1984:81:7194-7198 and Kieny, M.P. et al., Nature 1984:312:163-166. The ERA-G recombinant vaccinia virus has been inoculated to vaccinate various animals against rabies, including bovines, or by feeding the recombinant to foxes and raccoons. The possibility that a recombinant vaccinia virus might be introduced into nature, however, has raised controversy largely because of the rare side effects in people that are associated with primary smallpox vaccination with vaccinia virus. Furthermore, the vaccinia: ERA-G recombinant uses vaccinia virus Copenhagen, a strain that has been associated with relatively increased side effect rates in humans when used during mass vaccinations against smallpox and increased virulence for laboratory animals as described by E. Krag-Anderson in Proceedings of Sypmposium on Smallpox 1969, pp. 53-64, B. Gusic, editor, Yugoslave Academy of Sciences and Arts, Zagreb, 1969 and by M.F. Polak in Symposium Series in Immunobiological Standardization: R.H. 1973:19:235-242 Regamy and H. Cohen, editors, S. Karger Publishing, Basel.
In order to overcome problems associated with use of relatively invasive strains of vaccinia virus like strain Copenhagen, six different chimeric plasmids for regulating different levels of expression of G protein of the CVS strain of rabies virus have been produced and disclosed by Esposito et al. Virus Genes 1987:1:7-22. These plasmids are for inserting nucleotide coding sequences of G protein into the viral TK locus of the New York Board of Health (NYBH) strain of vaccinia virus. This strain demonstrated relatively low side effect rates in people during mass vaccination programs. In the six different recombinants that were produced, vaccinia virus promoter P.sub.7.5 which is an early/late class promoter or P.sub.11 which is a late class promoter were used to drive expression of G protein. As described by Esposito et al., Virus Genes 1987:1:7-22, each of the six recombinants administered by intradermal scarification or by footpad injection protected mice against rabies challenge. One recombinant that was injected intramuscularly into five dogs provided protection against a lethal rabies challenge.
The industry is lacking a raccoon poxvirus as a substrate for inserting genes to provide a useful expression system. The known systems do not provide a recombinant raccoon poxvirus for expression of heterologous DNA such as rabies virus surface glycoprotein or recombinants such as raccoon poxvirus: rabies-G that can be produced by using chimeric plasmids, such as those with viral thymidine kinase flanking sequences and promoter sequences designed for production of vaccinia virus recombinant. The industry further lacks live raccoon poxvirus: rabies virus recombinants that can be administered as an oral bait-delivered vaccine to (1) protect raccoons and other wildlife species against rabies and (2) produce related immune-reagents and/or other types of veterinary vaccines.